1. Field of the Invention
The present invention is a process for manufacturing an oil-in-water type emulsified food and also an oil-in-water type emulsified food prepared by this process. The oil-in-water type emulsified food is preferably a semisolid, such as mayonnaise. The physical properties of the emulsified food exhibit little change during manufacturing, when made by the process of the present invention.
2. Discussion of the Background
Semisolid oil-in-water type emulsified foods such as mayonnaise are commonly made by mixing an aqueous phase material consisting of egg, vinegar, salt, seasoning, etc., and an oily phase material consisting of an edible fat/oil, thereby forming an oil-in-water type emulsified food. The compounding ratio of the aqueous and oily phases has been studied (see, for example, xe2x80x9cInfluence of Compounding Ratio of Materials on Properties of Mayonnaisexe2x80x9d, Kaseigaku Zasshi, vol. 31, no. 9, 1980). In general, it is known that increasing the amount of vinegar, or increasing the mixing temperature of the ingredients, results in a softer product. Consequently, the usual temperature which is suitable for manufacturing mayonnaise is 15 to 20xc2x0 C. (see, for example, xe2x80x9cKnowledge of Mayonnaise and Dressingxe2x80x9d by Tadahira Imai, published by Saiwai Shobo, 1993; xe2x80x9cKnowledge of Fat/Oil Productsxe2x80x9d published by Saiwai Shobo, 1977; etc.).
When the ingredients of the aqueous phase material are mixed, and then immediately thereafter the aqueous phase material is mixed and emulsified with the oily phase material, the viscosity of the resulting emulsified food increases significantly. This phenomenon is called xe2x80x9csetup.xe2x80x9d However, when this emulsified food is used (for example, poured into containers, incorporated into other foods, etc.), the viscosity decreases. In other words, the viscosity properties of the emulsified food made by this process are unstable.
Alternatively, if the ingredients forming the aqueous phase are mixed at a high temperature or for a long time, phase inversion of the emulsified product is likely to occur, and it is also possible that the emulsified product may become less stable. Therefore, in order to make an oil-in-water type emulsified food with a constant viscosity, it is usually necessary to manufacture the food at constant temperature, i.e., within a 15 to 20xc2x0 C. temperature range.
Japanese Patent Kokai Publication JP-A-04-316462 proposes a different process for manufacturing an emulsified food, in order to provide improved cold resistance. In this process, the aqueous phase is heated to a temperature range of 45 to 50xc2x0 C. and then mixed with an oily phase at around 50xc2x0 C. However, these higher temperature conditions are employed to melt oily phases which have a melting point of 0xc2x0 C. or higher. In addition, JP-A-04-316462 does not describe the mixing time nor does it describe or evaluate the effects of the mixing time on the stability of the physical properties of the emulsified product.
Alternatively, there are many proposed processes for stabilizing the physical properties of emulsified foods by adding a specific protein (see, for example, Japanese Patent Kokai Publications JP-A-61-141861, JP-A-56-151479 and JP-A-06-319477, etc.), an acid (see, for example Japanese Patent Kokai Publication JP-A-55-108260, etc.) or a thickener (see, for example, Japanese Patent Kokai Publication JP-A-05-146269, etc.) to either the aqueous phase or the oily phase. However, none of these processes provide an excellent emulsified product by mixing egg and vinegar (acetum; acetic solution); instead, they involve adding an emulsifier other than egg.
Consequently, there is a need for an oil-in-water type emulsified food product in which the aqueous phase contains egg and vinegar, and the physical properties of the emulsified product are stable. There is also a need for a method of evaluating such stabilized physical properties.
An object of the present invention is to manufacture an oil-in-water type emulsified food in which xe2x80x9csetupxe2x80x9d and phase inversion do not occur to any significant extent during the manufacturing process, and the physical properties of the product are stable during use.
A stable oil-in-water type emulsified food, preferably a semisolid emulsified food having an aqueous phase material containing at least egg and vinegar, can be made by emulsification of the above-described aqueous phase material with an oily phase material, when the oily phase material contains more than 20% by weight of a fat/oil having a melting point lower than 0xc2x0 C., and the composition of the aqueous phase, mixing temperature, and mixing time of the egg with the vinegar are controlled.
The stable oil-in-water type emulsified food of the present invention may be any oil-in-water type emulsified food product, such as mayonnaise, sauces (i.e, hollandaise), salad dressings, etc. The emulsified food may be essentially a fluid, preferably a semisolid emulsified food.
The term xe2x80x9cfat/oilxe2x80x9d means fat(s) or oil(s), fat(s) and oil(s), etc. The term xe2x80x9cfat/oilxe2x80x9d may include mixtures of fats, mixtures of oils, and mixtures of fats and oils. A fat is any glycerol ester of a fatty acid, and an oil is a water-immiscible liquid of animal, vegetable, or synthetic origin.
It has been found that the stability of the physical properties of the emulsified product can be improved by mixing the aqueous phase materials and oily phase materials for a short time within a relatively high temperature range, or by mixing the aqueous and oily phase materials for a long time within a relatively low temperature range. A useful index for the stability of the physical properties of the emulsified product is the percent change in elastic modulus during storage, Gxe2x80x2. The change in elastic modulus is determined by comparing the elastic modulus of the emulsified product measured during storage, and measured while using the product (e.g., when the emulsified product is poured into a container, shaken, or used in another process). An emulsified product has stable physical properties when the change in the elastic modulus is small.
A preferred process for manufacturing an oil-in-water type emulsified food involves emulsifying an aqueous phase material and an oily phase material having the compositions described above into an oil-in-water type emulsion. The egg and vinegar components of the aqueous phase are mixed under the following conditions:
a. When the mixing temperature, T, is 30 to 55xc2x0 C., preferably 35 to 50xc2x0 C., more preferably 40 to 50xc2x0 C., the mixing time t (minutes) may be calculated using the formula t=106xc3x97eaT. The coefficient xe2x80x9caxe2x80x9d has a value of xe2x88x920.2 to xe2x88x920.3, preferably xe2x88x920.22 to xe2x88x920.27, more preferably xe2x88x920.23 to xe2x88x920.261. When the mixing temperature is 50xc2x0 C. (i.e., T=50xc2x0 C.) for example, the mixing time is 2 to 10 minutes when a is within a range of xe2x88x920.23 to xe2x88x920.26.
b. When the mixing temperature is 0 to 15xc2x0 C. preferably 0 to 10xc2x0 C., more preferably 0 to 5xc2x0 C., the mixing time should be from 1 day to 1 week, preferably 1 to 5 days, more preferably 1 to 3 days.
When the mixing temperature is higher than 55xc2x0 C., there is a higher probability that egg proteins may be denatured. When the mixing temperature is lower than 0xc2x0 C., it is possible that the aqueous phase may solidify. Neither situation is preferred.
Improvements in the physical properties of the emulsified product may preferably be expressed by the change in elastic modulus (Gxe2x80x2) of the emulsified product. The change in elastic modulus is determined by first allowing the emulsified product to stand immediately after it is manufactured, then measuring the elastic modulus. The elastic modulus is then measured after applying a load to the emulsified product which is greater than or equal to the yield stress. The change in elastic modulus can then be determined by comparing the two elastic modulus measurements. The physical properties of the emulsified product may be considered to be xe2x80x9cimprovedxe2x80x9d when the change in elastic modulus is 10% or less, or more preferably, 5% or less.
In the process of the present invention, at least 20% by weight of the oil phase, preferably at least 40%, more preferably at least 60%, most preferably at least 80%, based on the total weight of the oily phase, should be a fat/oil having a melting point lower than 0xc2x0 C. Edible oils which are liquid at ambient temperature and which may be used as a fat/oil according to the present invention, are for example soybean oil, rapeseed oil, corn oil, sunflower oil, sesame oil and the like. Thus, an ordinary fat/oil which is available in large quantities and at a low cost may be used in the process of the present invention.
The oil phase may contain a fat/oil having a melting point of 0xc2x0 C. or higher, such as palm oil, provided that it is present in an amount of 20% by weight or less, preferably 10% or less, more preferably 5% or less, based on the total amount of the oily phase. Semisolid, emulsified oil-in-water type food such as mayonnaise have improved physical properties when prepared by the process of the present invention.
The product manufactured by the process of the present invention is preferably a semisolid oil-in-water type emulsified food in which an aqueous phase material and an oily phase material are emulsified in an oil-in-water type.
The materials and components which are commonly used in the aqueous phase material, may be, in general, egg yolk, whole egg, egg white and other emulsifying aids; salt, syrup, sugar, vinegar and other seasonings; peppers and other spices; and water and the like. These materials may be combined and compounded in many different ways depending upon the desired use and application.
The materials and components which may be used in the oily phase material, may include various kinds of animal and vegetable fat/oils and various kinds of oil-soluble and oil-dispersible materials. It is essential that the oily phase material contain at least 20% by weight of a fat/oil having a melting point of lower than 0xc2x0 C. The oily phase of the oil-in-water type emulsified food of the present invention should be present in an amount of 65 to 85%, preferably 65 to 80%, more preferably 65 to 75% by weight, based on the total amount of the oily phase and the aqueous phase, in order to provide a stable emulsified product.
Conventional processes for manufacturing an oil-in-water type emulsified food (see, for example, xe2x80x9cKnowledge of Mayonnaise and Dressingxe2x80x9d by Tadahira Imai, published by Saiwai Shobo, 1993; etc.) may be used, except the conditions for mixing the aqueous phase materials (i.e., mixing temperature and mixing time of egg with vinegar) should instead be those of the present invention.
For example, the aqueous phase materials, except for water, are mixed with and dissolved in water, an oily phase material is added thereto and preliminary emulsification is carried out using a stirrer. Any suitable type of stirrer may be used, including those that impart either radial flow or axial flow (e.g., square pitch marine type impellers, fluidfoil impellers, etc.) to the mixture. Finishing emulsification is carried out using an emulsifier such as a colloid mill, homogenizer valve or xe2x80x9cliquid whistlexe2x80x9d device, thereby providing an oil-in-water type emulsified food.
In order to prepare the oil-in-water type emulsified food of the present invention, the aqueous material mixing temperature and the mixing time are precisely controlled, thereby providing an emulsified product which has stable physical properties. It is known that the emulsifying properties of egg increase, and the hydrophobicity increases, when the egg protein is denatured to some extent. But when the egg protein is excessively denatured, the emulsifying properties of the egg protein are lost. However, when the mixing temperature and the mixing time are controlled according to the present invention, it is believed that the egg proteins in the aqueous phase are optimally denatured, thereby suppressing changes in the emulsified state of the emulsified food after manufacturing, and contributing to the stabilization of the physical properties of the product.
As discussed above, the change in elastic modulus of the emulsified product may be used as an index of the stability of the physical properties of the emulsified product. When this index is small, the physical properties of the emulsified product are more stable. Accordingly, is easy to carry out preliminary experiments to measure the elastic modulus Gxe2x80x2, or to establish a calibration curve of Gxe2x80x2 at each mixing temperature when preparing an emulsified product.
Emulsified products made by the method of the present invention are stable and phase inversion rarely takes place during manufacturing. As a result, it is now possible to prepare an emulsified product having excellent stability.
The priority document of the present application, Japanese patent Application Serial No. 306645/1999, filed on Oct. 28, 1999, is incorporated herein by reference.